Many building fire and/or security systems (hereinafter referred to simply as security systems) are configured to contact emergency personnel (e.g., police, fire fighters, security officers, etc.) to report an abnormal or alarm event (e.g., a fire, a break-in, etc.) at a building. While some security systems are configured to contact the emergency personnel via a wireless or cellular interface, the majority use a public switched telephone network (PSTN), also known as a plain old telephone system (POTS), to contact emergency personnel. The security systems generally connect to a building's internal telephone network, and when a fire, break-in, or similar event occurs, the security system takes control of the PSTN, disconnecting all other devices connected to the PSTN. For example, if a user is using a telephone line (e.g., sending a fax, making a telephone call, etc.), the security system disconnects the internal telephone network, including the user, from the PSTN and takes control of the system to make its call.
FIG. 1 schematically illustrates a building 100 including a building telephone network 105. A plurality of devices 110 (e.g., telephones, fax machines, etc.) are connected to the wired telephone network 105. The telephone network 105 also connects to a PSTN 115 external to the building 100 through an interface 116. A security system 120 including a controller 125, one or more sensors 130, and a switch 135 is also connected to the telephone network 105 via a first connection 140 of the switch 135. A second connection 145 of the switch 135 is connected to the PSTN 115 through the interface 116. Thus, all of the devices 110 in the building 100 connect to the PSTN 115 through the security system switch 135. The security system 120 also includes a PSTN connection 150 connected to the PSTN 115 through the interface 116. When an alarm condition is detected by one of the sensors 130, the controller 125 “seizes” control of the PSTN 115 by opening the switch 135, and disconnecting the devices 110 from the PSTN 115. This “seizure” enables the security system 120 to contact authorized personnel immediately, even if other devices 110 are connected to the PSTN 115.
FIG. 2 illustrates a prior-art construction of a voice over internet protocol (VoIP) telephone system 200. The system is the same as the system shown in FIG. 1, except that the connection of the telephone network 105 to the PSTN 115 is severed (as illustrated by the “X”). In the construction shown, the telephone network 105 is connected to an analog telephone adapter (ATA) 205, which in turn is connected to a modem 210 (or computer). The modem 210 is then connected to the Internet 215. The ATA 205 and modem 210 form a VoIP interface 220 linking the PSTN devices 110 to the Internet 215, and enabling the devices 110 to communicate via the Internet 215 instead of the PSTN 115. The ATA 205 is configured to be installed anywhere on the telephone network 105, but in order to reduce installation cost and effort, the ATA 205 is often installed proximate the building's Internet interface (e.g., the modem 210).